Optic Chiasm

• After eye – axons (optic nerve) travel to optic chiasm
• Partial crossover of information
• Temporal side of retina – ipsilateral
• Nasal side of retina – contralaterail
• Becomes optic tract – still same ganglion axons)

After Optic Chiasm

• Tectopulvinar system – older system

• Geniculostriate system – majority of information

• Lateral geniculate nucleus of the thalamus

• Layers 1&2 – magno

• Layers 3-6 – parvo

• Layers 1,4,6 – left eye (for right LGN) - contra

• Layers 2,3,5 – right eye - ipsi

Primary visual cortex

• Visual area 1, striate cortex

• In occipital lobe

• Simple cells – edges/lines of a particular orientation/angle

• Complex cells – oriented edges and moving (at 90 degrees to orientation) – may also be motion specific

• End-stop cells – oriented edges of a specific length

V1

• Blob cells – color processing

• Interblobs

– Orientation and not color

• Eye dominance

• Column – one eye, one orientation, contains simple, complex, endstop

• Hypercolumn – region of cortex containing all 360 degrees of orientation for both right and left eye (about .5-1 mm square)

Tectopulvinar system

• Old system

• Motion, eye movements, attention, location

• Superior Colliculi (tectum)

– Multisensory area (touch, sound)

• Thalamus – pulvinar nucleus

• V2

V2 (all past this point also known as extrastriate cortex)

• Receives direct input from LGN and area V1

• Behaves and organized similar to Area V1

• Thin stripes

– Input from V1 blobs

• Interstripes

– Input from V1 interblobs

• Thick stripes

– Input from Layer 4B (magnocellular)

V3

• Receives input from thick stripe and interstripe areas of V2

– i.e., no thin stripe (Blob) input

• Generally color insensitive

• Edges of a particular orientation

• Small motion perception

• How forms are moving, rotating, changing

• Also depth perception

V4

• Inputs mainly from foveal regions of V1 and V2 (blobs/thin stripes)

• Perceived color of surface (not actual wavelengths entering eye)

• Lesions here lead to loss of color vision

– Cerebral achromatopsia

– Also difficulty accurately perc color under changing conditions of illumination

V5

• Middle/medial temporal cortex

• Input from thick stripes of V2 (i.e. Magnocellular)

• Specialized for detection of speed and overall motion of entire objects.

• Lesions lead to inability to perceive objects in motion

– Perceptions are frozen (Cerebral akinetopsia)

Temporal Lobe

• Inferotemporal Cortex

– Cells here have been reported that respond to a single complex stimulus such as an apple

– Lesions here leads to inability to identify an object (visual agnosia)

– Picking it up is no problem

• Superior Temporal Cortex

– Lesions here lead to inability to recognize faces (prospagnosia)

IT

• Primary cells – respond to simple stim

• Elaborate cells – shapes with color or texture, complex stimuli

• Size neurons

– invariant neurons – respond to obj no matter what size (near or far)

– variant – resp to spec sizes

• Location neurons – Where in visual field

• View neurons – viewpoint seen from

Parietal Lobe

• Lesions here leads to inability to determine relative position of objects.

– “Is the cup to the right or left of the spoon”

• Difficulty in using vision to reach object (optic axatic) and moving attention (visual neglect)

• No problems in identification

– “That’s a cup”

– “Can you pick it up?”

– “No.”

How know?

Evolution

Recordings from brain

Selective rearing - kittens, humans

Brain damage

Selective adaptation - humans

Experience on neural responding - monkeys, humans